Yahoo News

But would that mission do any science? And would it steal the New Frontiers budget?

http://www.planetary.org/blogs/casey-dreie...-the-cheap.html

To add to the above, it is not known if these plumes are cyclinic (they erupt every time Europa is in aphelion like a clockwork) or they are less irregular. Not knowing the answer leaves it less then likely a mission would ever get off the ground.

Hopefully JUICE can find an answer.

And try looking at our topic on the plumes in our other Europa thread. This topic and more has been discussed there.

I appreciate that Europa missions are amongst the most thoroughly studied in the catalogue of future unmanned spaceflight, but I was wondering whether there was any discussion of the trade space for the primary mirror versus shielding mass, mass, potential orbits, pointing issues, radiation and similar. I suspect this is probably because the answers are so clear as to be self-evident, and my apologies in advance.

LORRI-class optics seemed to provide encouraging results at a reasonable stand-off range in 2007. Are there any possibilities opened up by HiRISE or supra-HiRISE (e.g. 1m, or 1.2m mirror)? More distant fly-bys for equivalent resolution to the NAC/Topographic imager, or some kind of elliptical orbit which produced very close fly-bys (Recon Imager equivalent) and then kept the spacecraft out of the most hostile area for most of the time, and perhaps forestalled the need to dispose of the spacecraft while it was still functional for planetary protection purposes. Perhaps the challenge of motion compensation with no scan platform might make it infeasible even if the mass trade was not completely ridiculous.

It probably means no prospect for a radar instrument, and perhaps the scaling of the mirror is such that it is a catastrophically poor choice compared to shielding mass.

I struggle to see how NF-class mission would work, though the older IVO proposals for Discovery (admittedly with the power supplied via GFE) seemed to suggest it was not utterly implausible.

Anyway, apologies again if these are distracting from more salient questions on the prospective Europa mission.

Edit: Search function already had some leads on the various issues with this, and OPAG discussion c. 2004 - 2006 of special optics from Ganymede - it still seemed to hold some promise at that point. Presumably the trades have not changed appreciably since then, except perhaps the new explicit science goal for plume imagery/spectra.

Roly

I looked at various options that may be considered for a $1B mission: futureplanets.blogspot.nl/2014/01/europa-new-frontiers-mission-or-why-i.html?m=0

(Sorry, could not get the live link function to work on the antiquated phone that is my internet connection for the next while.) - Fixed (link, not your internet!) - Mod

Basically, the cheaper mission could fly fewer instruments, return less data per flyby (cheaper power amd comm systems), and/or reduce radiation harfening (which would reduce the number of flybys).

The minimum mission looked at by the Clipper team would carry just three instruments: a moderate resolution imager, an imaging IR spectrometer, and an ice-penetrating radar. All produce large amounts of data. A mass spectrometer would be the fourth instrument priority and essential for plume flybys.

For good global studies, the Clipper team analysis suggests that 20-30 flybys are needed by some study goals and up to 50 for others. By contrast, JUICE will do just two flybys and the proposed $1B Io multiflyby mission would do 6+ encounters of that moon.

Dear Van,

Many thanks for this - the post was precisely what I needed to read to get a sense of reasonable speculation as to how downscoping might work. The original radar seems very heavy c.f. modestly lower performance of the JUICE equivalent, which was interesting, as was the sharp decrement in cost (and key elements of the science) that accompanied the reduced flyby numbers of the decadal Io study and the JUICE planning. Even still, it was, in some ways, encouraging that a worthwhile mission was not utterly infeasible.

It appears that the distant special distributed optics design of the 2004 - 2006 era had that brief moment of efflorescence in the LPSC abstract and the OPAG presentations, and subsequently has not been the subject of much further pursuit (which perhaps suggests there were sound reasons to foreclose it as an option for Jovian exploration).

Thanks again for your précis here, and the Future Planets post,
Roly

I dunno if this is the right place for this... but what is the logic behind planetary protection for Europa? I had thought that the ice crust was at minimum 1 km thick... how could a reasonably sized spacecraft at orbital speeds possibly penetrate to an 'interesting' region?

Because the ice crust may be recycled over reasonable scales of time, or a given spacecraft may hit the jackpot & impact a surface weak spot…stuff like that. Bottom line is that we really don't have a great handle on Europa's ice crust dynamics as yet, nor if there even really is an ocean underneath…too many unknowns. Therefore, the smart move is to be extremely cautious.

Ah, OK, thanks... I just had seen stuff making it sound like it would be incredibly difficult to get through the ice intentionally (eg drilling lander) so it seemed like kind of a disconnect.

When you say recycled over reasonable scales are you talking millions of years (short compared to the age of the moon itself) or something much shorter?

I also believe that while Europa may recycle crust from the surface back into the interior, its surface coloration shows that material does come up to the surface from the interior. And (trying to phrase this acceptably), if a Europa probe finds anything interesting on the surface that could have come from within the putative deep ocean, you would want to be certain that it couldn't have hitched a ride on a terrestrial spacecraft.

-the other Doug

The age of Europa's surface is approximately 60 MYa. If we naively assume that it's being recycled systematically, one bit at a time, then you'd expect an object on the surface to go subsurface after an average of 30 million years. But if you shattered a space probe into many pieces, and you happened to hit a general region that was on the "short list" for subduction in the near future, and moreover the object was dark and metallic, so hotter each day than the ice around it, it might get subsurface faster.

To be clear, I don't think we'd likely have a crashed orbiter get into the ocean very soon with any great probability, but an ocean is exactly the sort of thing you *really* won't want to risk contaminating because of potential global mobility over short time scales.

Anything on the surface will be fried by the radiation just as thoroughly as if in Jupiter orbit, won't it? 30 million years of 5.4 sieverts a day? Even radioadurans would have trouble with that!
But, of course, better safe than sorry.

Yes, materials right on the surface of Europa would be fried by radiation, but such "frying" leaves a number of remnants which can tell you a lot about the original materials. Also, ice is an excellent radiation shield, so digging down into the ice less than a meter can give you examples of materials that haven't been fried. This also goes for hitchhiking terrestrial materials on a probe that happens to crash into Europa and are buried deeply enough in the ice to provide substantial radiation shielding.

-the other Doug

I see your point. I figured any future landings would be soft, so nothing could escape being sterilized, but of course landing rockets can and do fail. Flybys and orbiters seem like the way to go for now (just as Clarke predicted)!

Some years back I was contemplating the possibilities of very small & cheap spacecraft for deep space missions; communications was always the big stumbling block. Since I like playing Devil's Advocate, this led me to wonder: what if we don't need to worry about communication? Why not carry the data physically?

Envision something like a Cubesat with a basic telescope, solar arrays, and something like a tiny ion drive for attitude control and minimal course corrections, and coupled with a small computer and hardened flash drive (capable of surviving a high-speed reentry return to Earth). Envision a mission where you launch a dozen (or more) of these things towards Jupiter/Europa, with the spacecraft completely autonomous once launched. They loop past Europa on a close flyby of a region of interest, snap a few hundred images and store them on the flash drive, use Jupiter for a gravity assist and swing back towards Earth, eventually re-entering at a pre-specified longitude & latitude, and fall to the ground, probably transmitting an electronic ping (or sending a text message over the nearest cellular network). Someone just needs to pick them up and copy the images from the flash drive (or email them over a cellular network, no need to track it down), mission accomplished.

Extending the concept, a simple conventional lander might be sent to Europa, autonomously land on the surface and collect seismic and other data, then later send burst transmissions of this data to a passing autonomous Cubesat vehicles making close flybys as above, which then deliver the data to Earth.

All of this requires rather a lot of trust in autonomous navigation, but that's just a matter of software. In principal you could launch a hundred of these things for a fraction of the cost of a regular mission, with great redundancy.

Navigation isn't a 'matter of software'. It's a matter of the huge, powerful and complex infrastructure of the DSN combined with comms onboard a spacecraft used as two way and indeed three-way links and regular Delta-DOR for accurate navigation. Your proposal would require quite extraordinarily accurate gravity assist for the return flight to Earth ( if the E-J-E free return trajectory is doable without significant propulsive maneuvers ) - that level of accuracy can't be coded away - it requires ground-in-the-loop hardware, comms etc.

Moreover - name a spacecraft - any spacecraft - that flew as far as Jupiter and Back - without requiring human intervention due to safe modes, TCM's, etc etc.

It's a non starter.

First, a big round of applause for DSN Now. Everybody go look. I've just a small comment on getting low mass spacecraft back to Earth accurately from distant destinations. I think light sailing could play an important role here.

Doesn't matter if you get your delta-V from mono prop, bi prop, ion, solar sail...the navigation challenge still remains.

But saving all that mass by not carrying a gigantic HGA has to count for something, right? Galileo navigated just fine with low-gain only.
The main issues in that case would be limiting data corruption on the trip to Earth. And of course, waiting years instead of hours to find out if an experiment had a payoff will play havoc with blood pressure back home!

A lot of the mass in a telecom system is in the modulation and RF circuits. The "Small Deep Space Transponder" http://en.wikipedia.org/wiki/Small_Deep_Space_Transponder weighs 3 kg and doesn't include the output power amplifier.

Define a detailed mass breakdown with components you can actually buy and I'll believe it. Until then you're just writing science fiction.

Oh, I know it's all SF (per Doug's reply to algorimancer). The accuracy needed for some sort of 'free return' from Jupiter/Europa is implausible.
And honestly the best way to show that it can't work is the fact that no one's tried it yet in 50+ years (even from as close as the Moon!)

Actually, the concept of a self-navigating Earth-return planetary probe goes back to the late 1950s, when Charles "Doc" Draper (of the MIT Instrumentation Lab) was approached to design an auto-navigation system for a Mars flyby-and-return probe. The concept was a probe that would autonomously navigate itself to a Mars flyby, expose several rolls of film using automated cameras, and come back for an Earth return.

The probe never made it out of an early study stage, but Draper's early work on it evolved into numerous applications of inertial guidance systems.

-the other Doug

As far as maximizing science return for minimum cost, I've always liked the idea of a Europa flyby craft with high data rate sensors (e.g., high resolution) and a data recorder
of 10 terabytes or more. Do as many flybys as the recorder (and other mission constraints) allow, then boost the spacecraft to a high orbit, away from the intense
radiation. You could then take your time returning the data to Earth without the need for a return capsule or a large spacecraft antenna. Of course, laser communications
would make the whole idea moot.

Using what as a storage medium? Flash is quite radiation-soft and MRAM, while promising, is not dense enough yet.

I am not an expert in such things, but I was thinking along the lines of the Honeywell Aerospace Satellite Data Server.

See http://www.honeywell.com/sites/aero/Data-P...A6EC2FAE1F6.htm

It's radiation-hardened, but of course that's for the Earth orbit environment. Perhaps a combination of this design and spot shielding would enable Jovian operations.
The Honeywell product is 16 Tbits. I believe there are larger recorders, but they may be classified.

The lack of specs makes this hard to evaluate, but the box looks like it weighs multiple kilos and it doesn't say what memory technology it uses.

A typical box designed for the GEO environment will have a hard time at Jupiter without a lot of extra shielding. A lot.

My understanding is that the core spacecraft electronics are less of a problem than the sensor electronics. The former can be put inside a radiation shielded vault (think aluminum plates and surrounding fuel tanks). The sensor heads, on the other hand, must be exposed to the environment (although they can be shielded on sides other than their viewing outlet).

NASA is using a lot of the preformulation money to fund radiation hardening of the instruments.

Less of a problem, though getting non-volatile memory to survive is still a significant issue.

At any rate, we were discussing this in the context of a very small spacecraft. IMHO, this is simply infeasible with current technology for a whole host of reasons.

As for sensors, there's nothing I can say without getting into competition-sensitive areas. From an engineering perspective, I don't see a lot of rational and realistic system trades having been made as far as Europa missions are concerned.

Many thanks Mcaplinger, this was very interesting to read. That issue of storage seems to always be "very soon now", I seem to remember chalcogenide / phase change and FRAM being promised in the JIMO-era studies. On the trades, does the option of spending much of the time "standing off" at Ganymede with a suitably massive and impressive mirror make any sense? I only ever saw it proposed in those MIDAS slides, and they were build around what seemed to be special optics.

Not to me. Shielding is easier to make than big optics and may well weigh less.

If people want to get some insight into some of the engineering that goes into these sorts of missions, the JUICE proposal information is a good read http://sci.esa.int/juice/ JUICE is actually a fairly good start for a Europa mission, too bad they didn't pick our camera

My thanks for your appraisal Mcaplinger, that makes sense, especially if there is no striking advantage in mass (even more so if it is potentially less favourable for mirror c.f. shielding). I do look forward to reading the JUICE materials - and imagine that the camera you proposed for that was extremely interesting, given the quality of the track record.

What's in a name, the acronym for the JANUS camera is in Latin: "Jovis, Amorum ac Natorum Undique Scrutator."
Jovis mean Jupiter, Scrutator is nearly the same as the English 'Scrutinise' but after that I had to give up to the meaning.
Italian instrument so the name figures to some degree at least. =)

Related link, as for the selection of instruments DLR are happy to be onboard as well. German page.

Although it pains me to see Europa exploration further delayed, the situation persists that we're still in search of the right mission architecture for the realities of Europa. Some post-Galileo discoveries, mainly based on analysis of Galileo data, have upended what we might have previously thought would make a good next step.

IMO, given the ability to detect plumes, but an incomplete knowledge of their temporal patterns of occurrence makes planning the next mission an absolute non-starter. If the plumes occur at every apojove, that's one reality to plan for. If they occur at 10% of apojoves, with no apparent pattern, that's another reality to plan for. If in a decade we see them only a few times, that's yet another reality. There is no wise mission design for Europa that precedes this sort of knowledge.

JUICE is planned to wrap up its main mission around 2033. If the idea of waiting for that mission to end before planning the next one doesn't make you wince, you're very young and very patient. Maybe recon from Earth-based/orbiting telescopes can allow us to plan pre-JUICE, but that still calls for at least a couple of years of observations and analysis before we can plan the next step.

Maybe the best bet is to time a free-return plume-sampling mission to arrive when JUICE is active and use JUICE's observations to adjust the outbound trajectory to time a fly-through more favorably. I'm not sure, though, if such an option even makes sense in terms of engineering and orbital mechanics.

The analogy I would use is that if exploring Europa is chess, the plumes are the king. We can make plans for mapping and radar, etc., and focus on the rooks and queen, etc., but getting a sample of the plumes back to Earth is checkmate. If we can play for checkmate, we should.

I rarely disagree with John, but this is one time I will. We don't yet know that the plumes are real. The plume signal was at the edge of detectablity -- much like the measurements of ozone at Mars. Going straight to a sample return mission is premature in my opinion. We don't even have a good idea of particle size or density. If they plumes exist, it does not mean that they are connected to a deep subsurface source -- look at the explanations for the Enceladus plumes that do not require as subsurface ocean. Also, do the plumes occur every orbit or once a decade?

There are excellent reasons for flying a dedicated multi-flyby mission whether or not the plumes exist. The strategy that makes sense to me is a synergistic mission with JUICE. JUICE can do the global studies stand offstudies of the plumes with its UV spectrometer. However, it will be limited to a small number of flybys within a narrow range of Jovian longitudes. A Clipper-like mission can make many flybys and adjust its Jovian encounter longitude to match the peak plume output (assuming it exists).

I don't think that the discovery of plumes requires that the only mission that now makes sense for NASA is a sample return. In my opinion, do global surface studies as already highly prioritized, map the subsurface of the possible plume region to understand the source, include the mass spectrometer that is already a high priority for in situ measurements, and perhaps also include a dust counter and/or dust spectrometer to give us particle size. Once we understand the nature of the plumes and can place their source in context, we can plan an optimal sample return mission.

Ideally, we'd fly the survey mission this decade and if appropriate the sample return mission the next decade. But I don't agree on NASA doing no dedicated Europa mission until JUICE confirms the nature and sources of the plumes.

Even if they turn out to exist, there could indeed be other explanations, a magnetic field at Europa could for example focus charged particles from the extremely powerful radiation belts around Jupiter at the poles.

Some models that have been presented do take into account possible reservoirs of water encapsulated in the ice sheet on Europa.
A water plume might originate in one such reservoir and so be of less interest, especially in providing any answers for the eventual habitability of Europa.

And indeed Enceladus is a good example for more reasons than that, we should remember how long it took before the final proof arrived in that first blurry backlit image in 2005.
Even though the report on possible water plumes is very interesting, it is quite too early to spin doctor / build a mission to sample any possible plumes from the meagre data we have.

I am all in favour of a mission to Europa, JUICE will take its time to get built and sent there. And we can only hope it will provide the answers to this question as to so many others we have.

Especially because you get situations like Titan. Now that we know a lot more about the surface, we seem no more likely to take another more informed look. And the nature of things is not that you can cache goodwill for forgoing a mission opportunity. You take it.

It's not that we should plan a sample return, but we should extend at least the techniques used to detect the plumes into a broader survey before a plan.

If further observations find limited or no recurrence of the plume, then a sample return would be either a bad prospect, a risky one, or a complicated one. Still, such observations are of low cost compared to the cost of a mis-designed mission.

Jupiter is passing one season of opposition now. I'm not sure the quality of observations made this year. Hopefully this and/or the next opposition will yield some good follow-up to help pin down the question. So far, we have only two seasons of observations with any data reported, and whatever the cost (and potential ambiguity) of more observations, it's worth observing first, planning second.

http://solarsystem.nasa.gov/europa/sdt2013.cfm has a bunch of reports and other information from the Europa SDT, and is useful background reading if you're interested in Europa mission architectures.

The Planetary Society is reporting today that a (non-landing) Europa mission will be funded:

http://www.planetary.org/blogs/casey-dreie...opa-fy2016.html

ce

Looks like a lander of some sort is still a possibility:
http://blog.chron.com/sciguy/2015/05/a-eur...-to-support-it/

Yep -- that's Adam Steltzner, of MSL landing fame, up there energetically (as always) describing JPL's ideas on building a Europa lander, complete with a melting mole to try and access open water or at least deep ice. Interesting to look at the notes on the board, the flip chart, and the PowerPoint page hung on the board at the far right of the picture.

-the other Doug

That in itself not new, though. NASA recently (March or earlier) invited ESA to provide a lander to the Europa Clipper.


Edit: changed month

News Conference coming up later today on NASA TV. Time is in EST:

2 p.m., Tuesday, May 26 - NASA News Conference on the Selection of Science Instruments for the Europa Mission (all channels)

Another stream starting here too: https://www.youtube.com/watch?v=ivHHFoKn2pU

Interesting news conference overall on the instruments. Just a passing reference in response to a question about studying a lander. Studies on that are in progress and should be finished later this year.

I just read the blog posting on the instrumenta over on the Planetary Society website. Nine instruments on this mission. Wow. I know it is considered a Flagship mission, but with all the talk of trying to keep mission costs down I expected a bit smaller payload.

Not that I am complaining.

The item that really caught my eye was the EIS (Europa Imaging System).
- Near global coverage at 50 meters per pixel, and selected areas up to 100 times higher. -

My back of the envelope math comes out to highest resolution images being a half meter per pixel. Very nice.

Well, think about it. If you're prospecting for the best places to melt through the ice down into the Great Ocean, you need to characterize the surface on a global scale. You can't run your ice-penetrating radar and sounding radar globally, so you have to have good enough photo coverage to match visual characterizations to the deep-structure information you get slices of from those lower-resolution, more limited coverage instruments. Then you can apply those matches to figure out all of the good potential ocean entry points, where the ice crust is the thinnest.

I would be really surprised if there aren't good visual cues in the high-resolution images of the surface that correlate to the thickness of the crust beneath. It might take some analysis, and the cues might be subtle. Bit I bet we'll find them.

Now, this all makes sense if you're using the next mission to plan your assault on the Great Ocean with a melting probe. If you're planning on bringing your melting probe with you on this next flight, well -- good luck finding a good, thin-crust spot to land it on within your mission timing constraints.

-the other Doug

I'm surprised that there is no laser altimeter in the Europa spacecraft payload. There's no indication of an altimetry mode in the radar instrument, so the mystery deepens. I was under the impression that determining the exact shape of Europa was important for modeling the tidal heating from Jupiter. It's possible to get some topographic information from stereo imaging, but it's hard to imagine getting the large area coverage with high resolution I think is necessary for detailed shape modeling.

I would think that altimetry information would be at least indirectly acquired by the radar instrument in any case, though. Perhaps it's just a matter of mining the data properly.

You can do a lot lot better with stereo imaging that you could ever do with 40 flybys with a laser altimeter.